@jgandalf1: "There is a chunk of quartz in our garden that came from the local area
(well, reasonably close). It appears unusual to me in that it is
rather vesicular. I don't recall seeing this type of composition in
quartz. The pores look similar to what one might see in pumice, except
they all are trending in the same direction. Actually, it looks as
though termites had invaded the rock. Our local geology (South
Carolina mountains) is weathered granitic gneiss, and so on. 
Is it possible that these pores are caused by gases, or is it an
erosional feature? At any rate, what would be the mechanism by which
they form?
As a final note, the porous area looks to be a bit more grey in color
than the rest of the rock, so possibly not quartz? (Felsic, perhaps?)
If needed, I can take a picture, but I don't have a posting site, and
it'll have to wait until the rains stop (blessed rain in this area of
scary drought).
Thanks,
Joe"
    @jgandalf1: "On Sat, 27 Dec 2008 13:48:22 -0600, Jo Schaper
<quote>
Thanks, Jo. I'll try to get some shots within a week. 
I will mention that the stuff is quite white, with the "grey" part
only less white. (Of course, right now it's all dark, but in the
morning I will fetch it in.)
Joe"
    @jo34schaper31: "<quote>
Can't say I've *ever* seen cave travertine with gas vesicles arranged as 
you say, Bruce.  Have seen quartz crystals with same, but not from SC. 
Not to say they don't happen but relatively pure travertine has a 
whole ream of other more characteristic properties: very soft, shaped as 
botryoids, dripstone or flowstone, Calcite crystals  radially set or 
vertically elongated in bunches beneath a flowstone surface(not that 
differently than chalcedonic quartz coatings, actually although the 
hardness, luster and the fracture (flashy rhombs vs glassy  conchoidal 
semi-circles or an uneven,flaky, satiny surface for quartzite) are all 
giveaways. The other giveaway is: if travertine is    outside for more 
than about a year, it loses its luster entirely, and  becomes flaky and 
dull as it dries out. For quartz, this rarely happens in under a human 
lifetime. Travertine (or its surface variant, tufa) wouldn't even be on 
my checklist for Joe's rock unless the rock were quite soft.
As far as directional holes, some limestone with wormtracks in them 
weather out the wormtracks, leaving lines of holes in the rock around 
  here we call these fairy rocks (after Tinkerbelle and the garden fey, 
with no aspersions or reference to human sexuality.) Some Cambrian 
sedimentary chert (Potosi quartz druse) is pockmarked with holes, and 
the same could be said, as you note, of igneous rocks with pisolites 
(ash fall ignimbrites are notorious for these, where a bit of pumice 
falls into a reactivated ash flow and hardens, but the pumice then 
easily washes out after a few million years. There are even micas where 
the garnets have eroded out, or ashfalls with iron amygdules missing, 
which look pockmarked.
The scratch test is more characteristic than the fizz test when it comes 
to dolomite vs quartz...I've seen oodles of micritic dolomites which 
don't fizz at all at room temperature, even under a hand lens. I've even 
seem some claystone, but technically still limestone, which barely 
fizzes. That's why provenance is important, and pictures almost nearly 
so if one doesn't have the specimen in hand."
    @jo34schaper31: "Joe this is a carbonate diversion. We're still happy to take a look at 
  the photos.Disregard unless you're interested in carbonate debates *|:-)
Jo
<quote>
No, that's me, with my undergrad thesis on freshwater tufa deposition in 
the Ozarks, and mud in the blood. The difference may be one of those 
"English language split by a common tongue" sorts of things: Classic 
Roman travertine such as your image is the same sort of foamy, fast 
growing, quite soft, superficially pumice-like carbonate as what goes by 
the name tufa or marl around here. I quite agree the type locality for 
travertine, of volcanic hot spring origin, doesn't resemble what cavers 
  call travertine at all, except at Mammoth Hot Springs in Yellowstone, 
where the actively depositing calcite is actually a hard, shiny, banded 
stone forming crystalline surface shapes very similar to cave speleothems.
When I started plowing through travertine/tufa literature for my thesis, 
I confused myself so often over who was actually talking about what 
rock, that I made an idiosyncratic decision: If it were hard, visibly 
crystalline, shaped like stal, or banded (includes "cave onyx" 
figurines) and made a ringing sound when tapped, it was travertine. If 
it deposited like cave stal into pearls, and flowstone, but was soft, 
somewhat porous, contained lots of clay/mud/organic matter due to fast 
deposit, and really crumbly (almost powdery) when it dried, but 
maintained its shape, it was tufa. Some tufa does contain vesicles, as 
Bruce says, often from decomposing gases from the trapped organic 
matter. If it were randomly shaped dirty flakes,(like from my water 
heater)relatively unconsolidated calcareous mudstone, more resembling 
shaly bits than a discrete rock it was marl. And if it were other 
calcareous scum like blocks my sink screen,and forms in the tub,it was 
ok to get rid of it!
I have no idea what to call stal which from from leached concrete. Some 
people call them "bridgites." And I've seen silica geyserite called 
"travertine" too
This probably isn't standard carbonate nomenclature, but even various 
papers in the scientific literature define travertine, tufa and marl 
variously, and it seems to depend upon local usage.
What a diversion from the original question! Sorry, Joe.
This is good.
Long years of looking at really messed up Lower Carboniferous 
(Mississippian) carbonates with very few crystalline limestones, but 
lots of marl, marlstones, argillaceous limestones, sandy limestones,limy 
  sandstones, rocks which varied in the same layer from limestone to 
dolostone, sandy dolomite (where the "sand" is dolomite crystals) with 
carbonate stromatolites, chert stromatolites, both carbonate and chert 
algal reefs, limestones with/without fossils, dolomites with fossils (in 
the dolomites, not just those in the chert) and apparently cherts formed 
from   fine grained limestones and dolomites as well as vice versa, 
(ever seen a fizzy weathered chert rind? That's something strange!) 
makes me look at all this stuff as a continuum, instead of discrete rock 
types.
After the scour event on my study site,I saw vesicles in broken rock, 
but assumed the CO2 was mostly from the organic matter decomposing.  I 
also know where there is a lake tufa from the Pleistocene, mounded up 
with all sorts of non-fossilized bones in it...that stuff (shoreline 
deposit) is really fluffy, calcite frozen foam, too."
    @see_real_one: "On Mon, 29 Dec 2008 12:25:20 -0600, Jo Schaper
<quote>
<snip>
I'm interested in damn near everything. 'Cept competitive sports; big
yawn there.
Computer took a nose dive on Xmas, just now surfacing (Linux is
looking better all the time). Couldn't even play with the shiny new
monitor for 5 days.
Now that the sun is shining, I'll do my best to get a few pictures up,
with a scale ref as well. 
Another question: As chemical supply companies increasingly are
looking out for our well being by not selling us *anything* (even
NaCl), what is a good dilution to use for Muriatic acid, such as is
sold for pool cleaning? Is the supplied strength sufficient, or what?
Thanks so far.
Joe"
    @jo34schaper31: "<quote>
No kidding...got into geology, because it was more interesting than 
watching/playing sports involving a designated field, and *.*ball.
My next computer will likely be either an OSX Mac or a Linux box. My 
brother has a cute 16GB flashdrive 6"X9" tiny laptop running some flavor 
of Linux, and Open Office, and still has most of his tiny flash drive free.
I checked downstairs. Don't have a pool, but we use that stuff to clean 
bathroom and kitchen fixtures here in hard water land (don't get me 
started on water softeners. Hard water is *good* for you! Low sodium,and 
all that *|:-) My pool cleaner is 31% HCL...dilute it 1 part into 2 
parts water to make about a 10% solution, and it will fizz good enough 
without doing a number on your clothes if it splashes. I have my HCL in 
a tiny squeeze bottle the kind nose spray comes in. If you reuse such 
a bottle, CLEARLY mark it HCL and keep it away from kids and stupid people.
The school I taught Geo 101 lab for and I tangled a bit even using 10% 
distilled white vinegar was forbidden for fizz tests, unless you had 
hazmat training and used gloves and eye protection. You could go to the 
cafeteria, and eat the stuff on salad, but you better not be caught 
putting it on rocks....
I love chemistry...can't wait to see the pictures"
    @jgandalf1: "OK, I finally got some photos up. Find 'em here:
<url>
The site puts them in the reverse order to what I would expect, so
start with the right hand picture. The leftmost is a photomicrograph
of the area under the text box on the previous pic. FOV here is about
2 cm.
Did I do OK?
Joe"
    @jo34schaper31: "<quote>
Pictures look fine. Did you try the muriatic acid yet? OR scratching it 
with a pocketknife?
Superficially, the two closest things the photos look like are a quartz 
(?) version of the chert cryptozooan reef structures we have around here 
(Cambrian, early Ordovician in age) or some sort of wormtrack structures 
eroded out of limestone (very close in morphology) and then silicified, 
although how I'm not sure this could happen. Or my first guess weird 
slag. Do you have any idea what the age of nearby rocks are?
Definitely looks more like quartz than calcite.
Wish photos 3 and 4 were larger. Photo 5 looks like limestone where the 
quarter is, and silica elsewhere,  so I would test both for fizzy. 
Trouble is, this mix of chemistry may occur both in an algal reef 
structure which is partly silicified or chertified, and you guessed it, 
  in slag with part glassy and part hardened flux (limestone.) What is 
the reddish stuff in the pockets like? Have you taken a magnet to the 
rock, to check for magnetic iron?"
    @see_real_one: "On Fri, 02 Jan 2009 19:57:13 -0600, Jo Schaper
<quote>
Thanks, Jo. I'll get the acid today, and bring the rock back in for
testing. Funny thing, but my wife got tired of seeing it sitting on
the kitchen table. The table itself is terrazzo, so it's not like we
don't already have rock there. (OK, in fairness to her, she's usually
very tolerant to pretty enthusiastic about rocks as well.)
Joe"
    @jeanlenior: "Bruce Bathurst a �crit dans le message ...
<quote>
You don't need hydrochloric acid, which was chosen arbitrarily and is
dangerous. It emits fumes of HCL gas, which are poisonous, and rather
discourages one's examining closely just what is fizzing with a
magnifying glass or geologist's lens. :-)
Lemon juice or vinegar were typically used by geologists.
Bruce
PS. In the field, I preferred not carrying hazardous liquids in my
pocket, so I substituted a little glass vial of fine oxalic acid
crystals. This I sprinkled on a drop of well-placed water. Its low
vapor pressure (lack of fumes) allowed me to examine the spot closely
with a lens. This was the standard technique of 19th Century field
geologists, I believe.
A 10% ( plus or minus) solution of HCL is standard for field testing.  It is
not hazardous in the amounts carried by a geologists (approx.10-20 ml )  nor
will a drop or two on a rock produce enough fumes to be of concern to even
the most sensitive.  The amount of "fizz" produced on a rock sample at the
stated concentration is somewhat diagnostic.  In the old days when
pharmacists mixed compounds you could ask one to make you a 10% solution, no
more sadly. Hydrochloric acid is sold in hardware stores under the name of
muriatic acid.  Often the concentration is given in degrees baum�.   18
degree baum� is approx. 28 %.  Diluting with
with 2 parts of water to 1 part of the acid will get close enough for a
field test.
JL"
    @jo345sch765aper: "<quote>
As I noted somewhere else in the thread, I just carry a old OTC nasal
spray bottle with HCL clearly marked on it, I double bag it in ziplocks,
and it's in the pack, not on my belt. Never had an issue with it, since
that tiny squeeze spray hole is going to drip at best, even if the screw
on cap came off.
Most of my field work is done in Paleozoic (Cambrian-Mississippian, 
occasionally Pennsylvanian) carbonates which are an
insane mix of of limestones, secondary dolostones, mudstones and thin
crumbly shales. The sandstones are pretty discrete; but the other three
sometimes interlayered and gradational. For the most part, the rock
units around here are named as Potosi Dolomite, St. Louis Limestone,
etc., so you would think knowing what unit it is in would be diagnostic, 
but because the dolostones are of the replacement variety, actual 
lithology varies quite widely. It is fairly easy to tell the limestones 
from the dolomites by texture; once you get the sparry limestones out of 
the mix, most of the limestones (grading into mudstone) are powdery, and 
rather soft; the dolostones are gritty, compact and generally harder. 
What confuses things even more are those incompletely dolomitized; it's 
not that unusual to have fossils retained in the dolomite i.e. the 
rock will not fizz, it's not shaley or muddy, but is carbonate and has 
fossils in it. I've also picked out limestone exposures in putative 
dolomites the book and the map says it should be dolomite, but it 
fizzes like crazy. What prompts me to test such rock? Its texture and 
eyeball muddiness.
I'm sure this method is non-scientific, and I don't expect it to work in 
an unfamiliar area, so I'm not advocating it. But that's what I like 
about geology every time you put information in little boxes, some of 
it thumbs its nose at you and does the Nah-Nah-Nahnahnah! dance."
    @jeanlenior: "Jo Schaper a �crit dans le message ...
<quote>
Standard for geologist worldwide is a 10% solution of HCL. A 1 molar
concentration which is sometimes used in soil science will generally not
react with dolomite. Even with a 10% solution the dolomite must be scratched
or powdered. Household vinegar used drop wise on limestone will not work (as
a rule) it must soak the sample. Just to make sure I tried using fresh lemon
juice on a almost pure limestone sample with no visible results. I would be
curious to know where in the literature is the use of oxalic acid crystals
recommended.
Here are some links that may be of use.
<url>
<url>
<url>
atherLabs.pdf
<url>
Scientific discussion: Upon reaction with 10% hydrochloric acid, ...
Geologists use this behavioral difference as a field test to discriminate
between ... <url>
Someone reminded me that in the USA often the muriatic acid is sold as 22
degree baum� . This is 36% (11.64) molar . To get 10% (2.87M) add 258 ml of
the 36% acid to distilled water then dilute to 1000ml. If you have Chemical
company concentrated HCl that will be 12 molar. For a 3 molar concentration
(close enough for field work) just dilute by a factor of 4 or 250 ml in
distilled water then diluted to 1000ml.
JL"
    @jo34schaper31: "<quote>
The formation names are what they are, and around here they include the 
lithology, unless they consist of known mixtures of the base rock. The 
Bonne Terre, is the Bonne Terre Formation, because it is a mix, and 
everyone recognizes it.
Originally, these all were called 1st, 2nd, etc magnesian limestones. 
However, the term magnesian limestone to me is indistinguishable from 
secondary dolomite. With one possible exception, none of the Missouri 
dolomites are primary dolomites. No one locally uses magnesian limestone 
any more, as that term is 100 years out of date."
    @jo345sch765aper: "<quote>
Well, you've pretty definitely determined that it is silica of some 
variety. The only silica I've ever seen that fits your description is 
sinter or geyserite some sort of hydrothermal quartz. Hydrothermal 
quartz requires hot springs or geysers. Any sort of geothermal/faulting 
in your immediate area? (I saw the note on the Brevard Fault, but that 
seems pretty far away.
Geyserite forms the same sort of shapes that travertine does  cave 
formations, et al  but it's quartz. Quartz melts at 820 degrees C 
the gray getting darker could just mean it is more porous, and it's 
filling up with water.
It sounds like quartz, all right. The question of how it got there is 
still a little hazy to me.
There were ancient seas in your area, but they are pre-Appalachian in 
agein fact, they formed the the rocks which were metamorphosed into 
the Appalachians.
If they are really thrust sheets, and not just erosion surfaces of an 
anticline/syncline, check to see if there is/how much displacement there 
is. This might indicate Appalachian orogen heating, but 800 C is pretty 
hot for non-volcanic surface deposits. The Norris Geyser Basin in YNP, 
which also lays down quartz sinter and geyserite has internal, near 
surface temperatures of about half that, according to the USGS. In that 
case, the superheated steam carries the silica upward, where it deposits 
almost immediately in the cooling spray at the surface. Sometimes it 
deposits in the tubes when steam builds below a plugged geyser tube, 
the darn thing explodes.
I've never seen quartz weather in this manner. I would go for initial 
formation, not weathering, assuming it was natural, or some sort of 
geothermal transformation.
It sounds like you're in a pegmatite area. You might look up 
metasomatism the alteration of rock by geothermal fluids, and see if 
any of this makes any sense at your location.
We aim to please with geology discussions. They are discussions, of 
course most geos learned long ago to disagree without being 
disagreeable. This has been an interesting problem to hack around on, 
Joe. Thanks for bringing it up."
    @libvet: "Joe <email_address> eyed the audience and in choked emotion intoned: 
news:<email_address>:
<quote>
You added a couple of interesting bits of information. It's unfortunate
you can't be more specific about where you collected this bit of rock, 
though even if you could that might not clarify things much. Still, the 
presence of the river, thrusts, etc. implies that not much of what you 
might find loose on the surface is specifically local but probably 
transported. You also mention breaking off pieces resulting in jagged 
edges. Do these appear to be crystal boundaries? How large are these edges 
or boundaries? If they are millimeter scale then the most likely 
explanation I could offer is that the rock is a metaconglomerate. The vugs 
would likely then be clasts of some more easily weathered rock type or 
mineral. If you don't want to just whack the rock with a hammer take a cold
chisel and chip off a piece on the least interesting face, it might reveal
unweathered clasts in a more pristine state. 
You also mentioned another rock with mica present. This is undoubtedly from 
a hydrothermal quartz vein probably unrelated to the rock you pictured in 
your images. Depending on the relative and absolute scale of the quartz and 
mica xtals I would hesitate to call it pegmatite but it is possible. Are 
there any feldspars present? Are there any small indications of the 
presence of sulfides or oxides? 
You also mentioned apparently botryoidal textures in some of the vugs. 
These are not likely to be primary but secondary textures usually the 
result of hydration of primary oxides but that is pure speculation on my 
part without being able to examine the hand sample. Goethite is the most 
commonly occuring example but manganese (and other) minerals can also take 
on botryoidal textures with hydration. 
I hope you continue to find the newsgroup useful.
Cheers,
Here we may reign secure, and in my choyce 
To reign is worth ambition though in Hell: 
Better to reign in Hell, than serve in Heav'n."
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